1. Field of the Invention
The present invention relates to a thin type fuse.
2. Description of the Related Art
Although current fuses and thermal fuses are widely used as members to protect electrical devices, thinning of these fuses is required for mounting space savings.
Therefore, a thin type fuse has been proposed in Examined Japanese Patent Publication No. Hei. 7-95419. As shown in FIG. 4A, FIG. 4B (a diagram of B--B cross section specified in FIG. 4A), and FIG. 4C (an underside view), swollen portions 21' and 21' are formed in the tip portions of a pair of band-like lead conductors 2' and 2' and put out from one side of plastic insulating substrate film 1' on to the other side thereof so as to keep watertightness, the tip portions of the lead conductors on the other side of said insulating substrate film 1' are connected by fuse element 3', which is covered with flux layer 5', and insulating covering film 4' is allowed to adhere to the other side of insulating substrate film 1' with flux layer 5' covered.
This thin type fuse has the following advantages. The introduction of the thin type fuse makes it possible to simplify the manufacturing process because of fewer stages in the process. In addition, the contact surface of the insulating substrate film with the insulating covering film is a flat surface without intervention of other members between these films and both films are bonded to each other at the contact surface by welding or with adhesives to easily keep excellent sealing properties against inner pressure produced by expansion of the flux on fuse-blowing, which makes it possible to protect a mist from flying in all directions.
A current fuse or thermal fuse works when the fuse element reaches its melting point by Joule heat stemming from an overcurrent or by overheating from the outside, thus to fuse. On the other hand, these fuses are required not to work by transient pulse currents developed on on-off switching.
The results of tests carried out by the present inventor indicate, however, that in the above-mentioned thin type fuse, transient pulse current-flow repeated a large number of times causes a change in fusing characteristics or breaking of wire, depending on the distortion of the fuse elements, so that use of this thin type fuse may lead to restriction of service conditions.